4-[(Aminocarbonyl)amino]-N-[(9H-fluoren-9-ylmethoxy)carbonyl]-D-phenylalanine, commonly referred to as Fmoc-D-APC(urea)-OH or Fmoc-D-APH(CBM)-OH, is a non-natural, protected amino acid derivative. Its structure features a D-phenylalanine backbone with a urea-functionalized side chain (4-[(aminocarbonyl)amino]benzyl group) and an N-terminal 9-fluorenylmethoxycarbonyl (Fmoc) protecting group. This compound is a specialized building block primarily used in solid-phase peptide synthesis (SPPS). The Fmoc group is a standard, base-labile protecting group for the alpha-amino function, allowing for iterative peptide chain elongation. The unique urea-modified side chain introduces specific structural and functional motifs into the peptide sequence, which can be crucial for modulating peptide properties such as binding affinity, stability, or biological activity in drug discovery and biochemical research. As a protected and side-chain functionalized amino acid, it is a key reagent for constructing peptides with tailored properties for pharmaceutical and life science applications, including the development of peptide-based therapeutics, enzyme inhibitors, or molecular probes.